Among most animal species, humans included, females tend to live longer than males. A number of theories has been advanced over the years to explain this gender-based survival advantage. Now, new research from Japan suggests a reason that can be tested: women’s immune systems age more slowly. A research team at Tokyo Medical and Dental University analyzed blood samples from 356 healthy men and women between the ages of 20 and 90. In particular, they measured levels of white cells and cytokines, molecules that interact with immune system cells to regulate the body’s response to disease. As expected from prior research, the investigators found that white blood cells declined with age, but they also observed two key differences between the sexes: in men they recorded a steeper decline of T-cells that protect against infection and B-cells which secrete antibodies. They also found that the expected age-related increase in natural killer cells and CD4 T-cells, which attack invaders, rose at a higher rate in women than in men. Elsewhere, similar findings have been seen in mice. The study was published on May 15, 2013 in Immunity & Ageing.
My take? This interesting new finding may help explain an age-old mystery. We know from studies in rodents that the cells in the female body seem to repair damage better than those in male bodies. Women also have a survival advantage because they develop cardiovascular disease about 10 years later in life than men, often in their 70s and 80s rather than their 50s and 60s. Women may also have an evolutionary based biological advantage because the female role in reproduction is vital to survival - not only do women give birth, but they nurse their babies and care for them during their early years. Men’s role in reproduction is limited and, for that reason, longevity in men may not be as vital to the continuation of the species. While women may benefit from qualities inherent in their genetics, none of these natural advantages guarantees longevity against poor lifestyle choices. A case in point: smoking rates and the risk of lung cancer have been rising in women, and lung cancer has surpassed breast cancer as the leading cause of cancer deaths among women in the U.S.
Katsuiku Hirokawa et al, “Slower immune system ageing in women versus men in the Japanese population,” Immunity & Ageing 2013, 10:19 (May 15, 2013)